1除以5-x+2除以4-x+3除以3-x=-3
问题描述：
1除以5-x+2除以4-x+3除以3-x=-3
答
1/(5-x)+2/(4-x)+3/(3-x)=-3
1/(5-x)+2/(4-x)=3/(x-3)-3
[(4-x)+2(5-x)]/[(5-x)(4-x)]=[3-3(x-3)]/(x-3)
(14-3x)/[(5-x)(4-x)]=3(4-x)/(x-3)
(14-3x)(x-3)=3(5-x)(4-x)²
-3x²+23x-42=-3x³+39x²-168x+240
-3x³+42x²-191x+282=0
(x-6)(-3x²+24x-47)=0
x=6或(-3x²+24x-47)=0
(-3x²+24x-47)=0
-3(x-4)²+1=0
(x-4)²=1/3
x=4±√3/3
所以x1=6,x2=4+√3/3,x3=4-√3/3